The hard disk drive (HDD) for a disk of 3.5 to 1.8 inches or even 1.0 inch or less has been used in various fields of automobile products, home electrical appliances and audio appliances, etc. Therefore, the reduction of cost of hard disk drive and the mass production thereof have been requested and the large memory capacity thereof has been also requested.
In order to satisfy these requests, there is a tendency that the high density recording magnetic disk medium of the vertical magnetic memory system, which has lately been put to practical use, has been employed in the above mentioned fields and spread rapidly.
The magnetic disk medium of the vertical magnetic memory system is used in a composite magnetic head (hereinafter referred to as a head) having a TMR (tunnel magneto-resistance) head or a GMR (giant magneto-resistance) head, which is a memory medium separable from the head by 10 nanometer or less controllably.
Such magnetic medium generally includes a glass substrate, a soft magnetic layer formed on the glass substrate and a magnetic layer provided on the soft magnetic layer. Discrete tracks are formed in a discrete substrate by etching the magnetic layer. (Incidentally, the term “disk substrate” is used as a material of magnetic disk to be mounted on a hard disk drive.)
The etching for forming grooves between tracks is formed through an uneven photo-resist film. The unevenness of the photo-resist film is formed by using the nano-print lithography and pushing the photo-resist film with an uneven stamper. The track width of the discrete track formed by the dry etching through the uneven photo-resist is 100 nm or less and the groove separating adjacent tracks is filled with a non-magnetic material in a later step. The technique of this kind is described in JP-2007-012119A and JP-2007-149155A, etc., and well known.
The magnetic disk of this kind is called as a magnetic recording medium of the discrete track system (DTM) and is currently paid attention to a technique capable of realizing ultra high density recording exceeding 1 terabit (inch2) for 2.5 inches several years later. Further, the bit patterned medium (BPM) having discrete tracks, which are finely separated magnetically in the track direction, has been entered into the practical implementation step recently.
In a usual DTM, a center of the DTM is eccentric with respect to a rotation center of a spindle and a center of discrete tracks formed in the DTM are eccentric with respect to the center of the DTM. Therefore, the tracks formed in the disk become eccentric with respect to the rotation center of the spindle unless the eccentricity is corrected stepwise.
Therefore, the head accessing tracks of the DTM can not trace tracks unless the ON track servo control is performed according to servo information. Since the servo information itself is provided correspondingly to respective sectors, the position of the servo information becomes eccentric when the tracks are eccentric. When the eccentricity of the track becomes large, the ON track servo control becomes indefinite and, therefore, the ON track control and the highly precise head positioning with respect to the aimed track, which is performed before the ON track servo control is started become impossible.
Therefore, it is necessary to perform a mounting position correction of a disk with respect to the spindle, in order to match the rotation center of the tracks with the rotation center of the disk (rotation center of the spindle). In an example of the track eccentricity correcting mechanism, a disk rotation center is matched with a track rotation center by moving a mounting position of a disk with respect to a spindle. However, the size of the disk rotating mechanism is large and, in order to set the amount of eccentricity to a predetermined value, it is necessary to perform the position correction of the disk several times.